I live in Germany on the western fringes of the Odenwald, the Forest of Odin, chief god of ancient Norsemen. The Odenwald is a wooded, mountainy region, desolate, lonely and almost evil if you try to venture far inside; but it is very beautiful.
But some 200 miles to the north is another mountain range, the Harz Mountains, and on their highest peak, the Brocken, there were strange happenings on this day every year.
Tonight, the eve of May Day, is Walpurgisnacht. It was believed in these parts that on this night witches and other evil creatures of the occult were free to roam the world and cast their nasty spells on poor defenceless people in their villages.
Often, 12 of the most wicked of their number formed a "coven" and led the celebration of a Witches' Sabbath, and their most important venue for this revelry was the summit of the Brocken.
Walpurgisnacht takes its name from St Walburga, an 8th-century English nun who devoted her life to the commendable objective of converting Germany to what she believed to be the true religion. She herself had no connection with the shadowy traditions of Walpurgisnacht. Her involvement is fortuitous, based on the coincidence that her feast day falls on May 1st.
The sinister aspects of Walpurgisnacht are based on its earlier importance as the eve of May Day, an important pagan festival. Even today, in many parts of Germany it is the custom on Walpurgisnacht to light bonfires to ward off all these evil spirits and to protect the locals from them.
But strange sights are still to be seen upon the Brocken. The "spectre of Brocken" is a simple optical phenomenon that can occur anywhere, but its appearance on the eponymous mountain was so common that it came to be associated with the place. It consists of a giant shadowy figure looming from the early-morning or late-evening mist.
The Brocken spectre is easily explained: it is simply the observer's own shadow, cast by the sun when it is low in the sky on to a bank of cloud or mist. Its mystique lies in its unexpectedness, and in its unfamiliar shape.
The apparition has a strange triangular appearance because, unlike most shadows we encounter, it is not localised on a particular plane surface; it is projected through the mist, and extends over a depth of perhaps 20 or 30 yards. Rays of light just grazing the body of the observer, and forming the edge of the shadow, are subject to the same perspective effect as railway lines, which seem to converge as they disappear into the distance.